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From: Thomas Munro <thomas.munro@gmail.com>
Date: Sat, 14 Feb 2026 10:58:50 +1300
Message-ID: <CA+hUKGKanfJD0fZghbDPTO96zkcw0ugpEuNZY90k7dk4dmUTfA@mail.gmail.com>
Subject: Re: BUG #19406: substring(text) fails on valid UTF-8 toasted value in
 PostgreSQL 15.16
To: Noah Misch <noah@leadboat.com>
Cc: ranvis@gmail.com, pgsql-bugs@lists.postgresql.org
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On Sat, Feb 14, 2026 at 6:27=E2=80=AFAM Noah Misch <noah@leadboat.com> wrot=
e:
> On Fri, Feb 13, 2026 at 07:46:22AM +0000, PG Bug reporting form wrote:
> > After upgrading from PostgreSQL 15.15 to 15.16, substring(text) raises:
> > >ERROR: invalid byte sequence for encoding "UTF8": 0xe6 0x97
> > on valid UTF-8 text stored in a TOAST-compressed column.
>
> > user=3D> select substring(data from 1 for 1) from toast_repro;
> > ERROR:  22021: invalid byte sequence for encoding "UTF8": 0xe6 0x97
>
> Thanks for the report.  That is a bug and a regression; I regret missing =
it
> during review.  The substring operation works by taking a 4-byte slice fr=
om
> the toasted value (4 bytes being the max length of a UTF8 char in Postgre=
SQL),
> the finding the actual first character within those bytes.  However, it
> incorrectly requires those four bytes to be a valid UTF8 string.  I'll st=
art
> on a fix.

Ack.  Also looking into this.